|Stage Name||Birth Name||Position||Birthday||Age||Height||Star Sign||C Y||BT Sort descending|
|Eunchae 은채||Kwon Chaewon||Vocal, Maknae||19||165 cm or 5'5"||Gemini||Hare|
|Jenny 제니||Lee Soyul||Visual||22||165 cm or 5'5"||Virgo||Rat||A|
|Yebin 예빈||Baek Yebin||Vocal||21||164 cm or 5'4½"||Cancer||Ox||A|
|Eunjin 은진||Ahn Eunjin||Dancer, Rapper||21||170 cm or 5'7"||Virgo||Ox||A|
|Chaeyeon 채연||Jung Chaeyeon||Visual||20||166 cm or 5'5½"||Sagittarius||Ox||A|
|Eunice 유니스||Heo Sooyeon||Vocal, Dancer||27||167 cm or 5'5½"||Virgo||Ram||A|
|Huihyeon 희현||Ki Huihyeon||Leader, Rapper||23||166 cm or 5'5½"||Gemini||Pig||O|
Dia 다이아 is a girl group formed by MBK Entertainment in 2015. The group's name is short for "diamond." It's also a backronym for "do it amazing," the name of their first album. The group consists of seven members: Eunice, Huihyeon, Jenny, Yebin, Eunjin, Chaeyeon, and Eunchae.
Their debut album, Do It Amazing, was released on September 14, 2015. On the same day, the music video for their lead single, "Somehow," was released. Their first official public appearance was also on September 14 when the group performed a showcase at the Ilchi Art Hall in Seoul. They made their official debut stage on the music program "M Countdown" on September 17.
On October 19, Dia released the music video for "My Friend's Boyfriend," another song from their debut album, and they continued their promotions for this new song on music stages.
On December 17, Cathy and Chaeyeon were announced to have temporarily withdrawn from Dia to join Mnet's girl group project show, "Produce 101." Both Cathy and Chaeyeon had auditioned and signed contracts with the show before Dia's official debut. Dia continued to promote as a five-member group. After being eliminated on episode 11, Cathy resumed her activities with Dia. Chaeyeon placed 7th in the final episode, which granted her entrance to I.O.I., and she continued her hiatus for ten months to carry out her activities with I.O.I. when the project group debuted in May. On March 7, 2016, MBK Entertainment announced the addition of a new member, Eunchae, and confirmed that Dia was currently preparing for a comeback.
On April 13, MBK Entertainment announced that Seunghee's contract with the company would come to an end on April 30, and she decided not to renew. On April 19, I.O.I.'s agency stated each girl's contract allowed for the possibility of activities under their respective companies while under the group, however indicating that, "I.O.I. will be promoting as a whole or in units for the upcoming 10 months." On May 11, MBK Entertainment confirmed that Chaeyeon and Cathy would return to the group for Dia's upcoming comeback. It was confirmed that Cathy would be using her real name, Huihyeon, and Chaewon would be using the stage name Eunchae for future promotions. On May 28, Dia performed with Eunchae for the first time in their appearance at the Youth Dance Festival.
Dia's first mini album, Happy Ending, was released on June 14, 2016. The group also released the music video for lead single "On the Road" on the same day, and had their comeback stage on "M Countdown" on June 16. On August 11, MBK Entertainment released a teaser for their Harry Potter-themed comeback. The group held a showcase for their second mini-album, Spell, at Blue Square Samsung Card Hall on September 12. The single "Mr. Potter" and mini-album were available for digital purchase on September 13 and physical purchase on September 21. On December 8, 2016, Dia announced that they would hold their first concert, First Miracle, on December 24 and 25.
In December of 2016, Dia released a pair of special digital single albums, each featuring a different sub-unit. First Miracle DIAID I dropped on December 29 with the single "You Are the Moon and Earth." It was from the A unit, also known as BinChaenHyeonCe for members Yebin, Chaeyeon, Huihyeon, and Eunice. The B unit, or L.U.B. (Lovely Unit B), consisted of members Jenny, Eunjin, and Eunchae. Their album, First Miracle DIAID II, featured the song "13/32." Both sub-units promoted on music shows in January 2017.